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Small blackberries usually come down to a handful of fixable issues, and once you identify the culprit, your harvest can bounce back fast.
If you’ve been asking, “Why are my blackberries small?”, the answer often starts with the age of your canes, the amount of sunlight they get, and how well you’ve been watering and feeding them.
Blackberries are generous plants, but they only reward you with plump, juicy fruit when their basic needs are met.
In this post, we’ll walk through the most common reasons your blackberries are small and what you can do about each one.
Let’s dig in.
Why Are My Blackberries Small?
Small blackberries happen for a reason, and it’s rarely random.
Understanding why your blackberries are small means looking at the plant’s health, its environment, and its natural growth cycle.
Here are the main reasons your blackberries aren’t sizing up.
1. Your Canes Are Too Old or Too Young
Blackberries grow on canes, and cane age matters more than most people realize.
First-year canes, called primocanes, usually don’t produce fruit at all.
Second-year canes, called floricanes, are the ones that bloom and bear fruit.
If your blackberries are small, you might be harvesting from canes that are past their prime or not quite mature.
The fix is simple: prune out the old canes after they finish fruiting and let new ones take over.
2. Not Enough Sunlight
Blackberries need full sun, ideally six to eight hours a day.
When they’re shaded by trees, fences, or even their own overgrown canes, the plant puts its energy into reaching for light instead of plumping up fruit.
That’s why blackberries in partial shade often stay small and sour.
Trim back anything blocking the sun and thin out crowded canes so light reaches the center of the plant.
3. Inconsistent Watering
Water stress is a huge reason blackberries come out small.
During bloom and fruit development, blackberries need steady moisture, about an inch of water per week.
If the soil dries out completely between waterings, the berries stop swelling and never reach full size.
Mulching around the base helps hold moisture and keeps the roots cool.
4. Poor Soil and Lack of Nutrients
Blackberries are heavy feeders, especially when they’re producing fruit.
If your soil is compacted, sandy, or low in organic matter, the plant struggles to take up the nutrients it needs.
Nitrogen encourages leafy growth, but phosphorus and potassium are what help berries size up and sweeten.
A soil test can tell you exactly what’s missing so you’re not guessing.
5. Too Many Canes Competing
Blackberry patches that aren’t thinned turn into a tangled mess.
When too many canes grow from the same crown, they compete for water, nutrients, and sunlight.
The result? Lots of small blackberries instead of fewer, bigger ones.
Keep only the strongest canes, spaced about four to six inches apart, and remove the rest.
How to Get Bigger Blackberries
Once you know why your blackberries are small, the next step is giving them what they need to size up.
These habits make the biggest difference.
1. Prune at the Right Time
Prune floricanes right after harvest, since they won’t fruit again.
In late winter, tip-prune primocanes to encourage side branches, which is where next year’s berries form.
This single habit is one of the fastest ways to fix small blackberries.
2. Feed With Balanced Fertilizer
Apply a balanced fertilizer in early spring as new growth begins.
Avoid too much nitrogen, which pushes leaves at the expense of fruit.
A handful of compost or well-rotted manure around the base also helps blackberries size up naturally.
3. Water Deeply and Consistently
Water deeply once or twice a week rather than lightly every day.
Deep watering encourages roots to grow down, making the plant more drought-tolerant and better at feeding large berries.
Drip irrigation is ideal if you want consistent moisture without wetting the foliage.
4. Control Pests and Disease
Spotted wing drosophila, aphids, and cane borers can all sap energy from your plants.
So can fungal issues like anthracnose and orange rust.
If your blackberries are small and look unhealthy, check for pests and treat them early before they spread.
5. Harvest at the Right Time
Blackberries don’t ripen after picking, so timing matters.
Wait until they’re deep black and pull free with almost no tug.
Picking too early gives you small, tart berries every time, even if the plant did everything right.
So, Why Are My Blackberries Small?
Small blackberries usually come down to cane age, sunlight, water, and nutrition, and most of these issues are easy to correct.
If you’ve been wondering why your blackberries are small, start by checking how old your canes are and how much sun they get.
Then look at watering, feeding, and thinning, since overcrowded canes are one of the most overlooked reasons blackberries stay small.
Fix these one at a time, give your plants a season to respond, and your blackberries should grow bigger, sweeter, and far more rewarding.